The present invention relates to apparatus for measuring the level and density of liquids.
The invention is related to application Ser. No. 07/484,295, now U.S. Pat. No. 5,077,482, by Victor Vali et al., entitled "Fiber Optic Fuel and Liquid Gauge" filed Feb. 23, 1990 and assigned to a common assignee with the present application. This pending application is incorporated herein in its entirety by this reference. The fiber optic liquid level sensor described in this pending application can be used as a leak detector for underground storage tanks, but only if the liquid temperature or density is simultaneously measured. This measurement is required to compensate for any change in the liquid volume not associated specifically with liquid entering or leaving the tank.
There are many previous techniques of measuring the temperature of a liquid, including thermistors, thermometers, thermocouplers, Mach Zehnder fiber optic thermometers, etc. The problem with these previous approaches is that the necessary accuracy for compensation of the density variation described above is very great. This requires heroic measures in fabrication and calibration.
Methods of measuring pressure accurately include Mach Zehnder fiber optic pressure gauges and piezoelectric devices. Again, the former is expensive to make and the latter measures only changes in time.
It is therefore an object of the present invention to provide a simple apparatus for measuring the density of liquids to compensate for the effects of density and temperature changes on a liquid level measurement.